If post-format == ‘gallery’ conditional

Question

This one’s an easy fix! The first argument in has_post_format() is a string in the format post-format-{type}, e.g. post-format-aside, or post-format-gallery, etc.

So, e.g., change this:

has_post_format( 'aside' , $post_id )

To this:

has_post_format( 'post-format-aside' , $post_id )

Wash, rinse, and repeat for all uses of has_post_format().

EDIT

Given your example code, I would even suggest another potential option, combining get_template_part() and get_post_format().

If you create template part files entry-aside.php and entry-gallery.php, along with a default, entry.php, then:

1) Move this code to entry-aside.php (and remove unsupported parameters):

the_excerpt();

2) Move this code to entry-gallery.php:

if ( has_post_thumbnail() ) {
    // use the thumbnail ("featured image")
    $thumb_id = get_post_thumbnail_id();
    the_post_thumbnail( 'thumbnail' ); 
} else {
    $attachments = get_children( array(
        'post_parent' => get_the_ID(),
        'post_status' => 'inherit',
        'post_type' => 'attachment',
        'post_mime_type' => 'image',
        'order' => 'ASC',
        'orderby' => 'menu_order ID',
        'numberposts' => 1)
    );
    foreach ( $attachments as $thumb_id => $attachment )
        echo wp_get_attachment_image($thumb_id, 'thumbnail' ); 
}

3) Move this code to entry.php

if ( $fluidtheme_options['fluid_post_content'] == "content" ) the_content(__('Continue Reading &rarr;', 'wptumble-fluid')); else the_excerpt();

4) Replace that entire if/else conditional block with this:

get_template_part( 'entry', get_post_format() );

Now, it might be overkill for your current use case – but the advantage is that, if in the future you decide to support other post format types, you simply have to add entry-{type}.php, and your template will already be set up to support it! For example, if you add support for quotes, simply add entry-quote.php, with whatever appropriate code, and you don’t have to change any existing code.